@John Nagle: Model 33 machines, like all the Teletype machines back to 1924, use standard Underwood typewriter ribbons. You can still get all the necessary supplies. See my page at "http://aetherltd.com/supplies.html".
Wait till you hear the sound -- when I get it fully up and running I'll take a video of it with sound. And if you are ever passing through Huntsville, Alabama, you'lll have tio drop by my office to see it and say hello.
>It's a 1979 vintage Super Elf based in the CDP1802
Mmmm...tasty. Never had much to do with the 1802s but I know a lot of people liked them. Maybe you should get it talking to Max's ASR.....
Ref the old mechanical teleprinters....they had some really clever ways of doing things then, but they were usually incredibly reliable. I once looked after a fleet of 6 T100 (mechanical) teleprinters for a year and a bit, and the most I had to do was replace a set of motor brushes. Siemens' successor to that machine was the T1000, all electronic, and we had so many problems with them. The ribbon direction-change mechanism in particular was a horror, finicky to adjust and very unreliable. Such is progress.
In the European-influenced world, teleprinters were almost invariably 5-bit Baudot, which is tricky to interface with computers. At least your ASRs talk ASCII which is intelligible to PCs with serial ports.
Great project - I'd be happy to set you up with a 232 to current loop converter to help you get that thing talking. Drop me a note at firstname.lastname@example.org. You'd be suprised how often current loop is still in use!
John - Thanks for the information. Upon a little more reading, it certainly does seem like it wouldn't be worth trying to build a converter. Although, it might be worth trying just for fun. I'd certainly hate to do something wrong and damage a 40 year old piece of equipment though.
Great information David. I actually have an old, old single board computer with a 20mA current loop. It's a 1979 vintage Super Elf based in the CDP1802. I have no idea if the current loop portion of it works though.
These early electro-mechanical or mostly mechanical devices like the ASR-33 are really fascinating. Funny that I see them as incredibly complex and almost beyond my comprehension, where a nice little MCU powered device, like a Beagleboard, seems relatively easy to understand.
For 20mA, buy a commercial converter. It's not worth the trouble of building one. I restore pre-WWII Teletype machines and build 60mA interfaces for those, but there, the current loop is really driving the selector magnet directly, and there's inductive kickback to deal with. The ASR-33 has a transistor driver inside; whether it's current loop or RS-232, it's just a signal, not electromagnet drive.
Model 33 machines, like all the Teletype machines back to 1924, use standard Underwood typewriter ribbons. You can still get all the necessary supplies. See my page at "http://aetherltd.com/supplies.html". There were at one time extra-heavy-duty ribbons for Teletypes, and although you can find those as surplus, they're too dried out to use today. Paper rolls are easy to get; paper tape is available but quite expensive.
It's even possible to reverse the yellowing of the plastic, which is a consequence of a bromine compound used during moulding. Look up "RetroBrite"
These machines are well understood, the documentation is available, and there's a discussion list ("Greenkeys Digest") for Teletype machines. I don't bother with the later models like the ASR33, but there are people on that list who do. The older models (1924 through WWII) are very rugged; I've restored four of them starting from fair to poor condition.